In some telecommunications applications a relatively broad frequency band may be divided into channels that may be assigned in such a way as to avoid interference within the transmission medium. For example, the data over cable service interface specifications (DOCSIS) allot the band between 5 and 42 MHz for “upstream communications from a cable subscriber to a cable television (CATV) “head end”. This frequency band may be used for a variety of purposes, including, through use of a cable modem, communications between a subscriber's computer and the Internet, communications to a CATV service provider, and digitized voice transmissions, for example. This 37 MHz upstream band may be divided into non-overlapping channels each having a bandwidth of approximately 3.2 MHz, 1.6 MHz, 0.8 MHz, 0.4 MHz, or 0.2 MHz. Each CATV head end may service as many as 20,000 subscribers and, consequently, with each cable acting a an antenna, and each cable connection “leaking” signal into the cable, the upstream band may be cluttered with interference. The upstream channels may be selected to avoid such interference, with, for example 0.2 MHz channels assigned with center frequencies set to fit in the interstices between interfering signals to thereby avoid interference. Channels having broader bandwidths might be assigned to frequency ranges of relatively low levels of interference.
Centralized headend and distributed headend communications systems are known and discussed, for example, in U.S. Pat. No. 5,841,468 entitled, SYSTEM AND METHOD FOR ROUTING DATA MESSAGES THROUGH A CABLE TRANSMISSION SYSTEM, issued to Wright, U.S. Pat. No. 6,100,883, entitled, HOME INTERFACE CONTROLLER FOR PROVIDING INTERACTIVE CABLE TELEVISION, issued to Hoarty, and U.S. Pat. No. 5,999,970, entitled, ACCESS SYSTEM AND METHOD FOR PROVIDING INTERACTIVE ACCESS TO AN INFORMATION SOURCE THROUGH A TELEVISION DISTRIBUTION SYSTEM, issued to Krisbergh et al, all of which are hereby incorporated by reference.
Upstream receivers typically devote a circuit board of electronics to each channel, and, within each circuit board, an analog to digital converter (ADC) to each channel. If any of those channels are unused, the associated ADC and ancillary circuitry is, in effect, wasted. Such waste may be manifested, not only in terms of capital outlays, but in the recurring costs associated with increased energy expenses, increased cooling requirements, and requirements for greater space to house the telecommunications equipment.
It would therefore be highly desirable to provide an efficient apparatus and method for receiving signals, such as DOCSIS upstream signals, whose center frequencies are distributed through groups of frequency bands.